An acceleration transducer, or accelerometer, is a sensor typically utilized for measuring acceleration forces. These forces may be static, like the constant force of gravity, or they can be dynamic, caused by moving or vibrating the accelerometer. An accelerometer may sense acceleration or other phenomena along one, two, or three axes or directions. From this information, the movement or orientation of the device in which the accelerometer is installed can be ascertained. Accelerometers are used in inertial guidance systems, in airbag deployment systems in vehicles, in protection systems for a variety of devices, and many other scientific and engineering systems.
Capacitive-sensing MEMS accelerometer designs are highly desirable for operation in high gravity environments and in miniaturized devices, due to their relatively low cost. Capacitive accelerometers sense a change in electrical capacitance, with respect to acceleration, to vary the output of an energized circuit. One type of capacitive acceleration transducer is capable of detecting movement along one or two axes that are generally parallel to the plane of the transducer package. This type of acceleration transducer uses a movable element that moves substantially parallel to a surface of the substrate to which it is mounted under x-axis and/or y-axis acceleration. Another type of capacitive acceleration transducer has a “teeter-totter” or “see saw” movable element configuration that is capable of detecting movement along an axis that is generally perpendicular to the plane of the transducer package. This type of acceleration transducer uses a movable element or plate that rotates under z-axis acceleration perpendicular to a surface of a substrate. Both types of accelerometer structures can measure at least two distinct capacitances to determine differential or relative capacitance.
Prior art multiple axis acceleration transducers typically have monolithic designs. In a monolithic design, the sensing structures are fabricated on the same substrate, or device wafer, in a planar fashion. Although die size reduction may be achieved by more efficient die area design processes, more aggressive fabrication processes, and so forth, there is a limit to the effectiveness of these processes without increasing manufacturing cost or sacrificing part performance.
Accordingly, there is a need for an improved MEMS acceleration transducer and fabrication methodology for overcoming the problems in the art as discussed above.